System and method for adjusting the low-frequency response of a crossover that supplies signal to subwoofers in response to main-speaker low-frequency characteristics

ABSTRACT

A system and method for adjusting a subwoofer sonic output in response to known main speaker characteristics in order to produce a desirable blending of sound from the combined subwoofer-main speaker output.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/849,633, filed on May 4, 2001, which claims the benefit ofU.S. Provisional Patent Application No. 60/207,790, filed May 30, 2000.These applications are incorporated herein by reference in theirentireties.

FIELD OF INVENTION

[0002] This invention relates generally to loudspeakers, and moreparticularly to a crossover or a frequency response shaping system foradjusting the frequency response of a subwoofer that, in conjunctionwith a main speaker, produces the sonic output.

BACKGROUND

[0003] As is well known, a loudspeaker receives an electrical signalrepresenting an audio sound, and converts the electrical signal to anaudio sound wave via a loudspeaker driver unit. The driver unitcomprises, in part, a motor that responds to the electrical signal tomove a diaphragm. The movement of the diaphragm perturbs the surroundingair, which causes the audio wave.

[0004] Due to inadequate low-frequency characteristics, manyloudspeakers do not respond well to input signals of very lowfrequencies (i.e., the bass or lower register). Thus, a high qualityaudio system may include a separate, specialized speaker, termed asubwoofer, which is designed to more accurately reproduce the lowerfrequencies of the full sound spectrum. This subwoofer may be used toreproduce the low-frequency portion of the same signal that is providedto the main speakers. In these applications, it is usually desirable torestrict the frequency range reproduced by the subwoofer to a range thatis not reproduced by the main speakers. Further, it is desirable thatthe frequency and phase response characteristics of the subwoofer beadjustable so that the outputs of the subwoofer and the main speakerwill combine in a desirable way (e.g. to produce a uniform frequencyresponse). Thus, the response characteristics of the subwoofer isintended to complement the response characteristics of the main speaker,hence, achieving a desirable blending of the sonic output (i.e., sound)of the main speaker and the subwoofer. Unfortunately, subwoofer controlsnormally lack the capacity to properly adjust the output to achieve asubwoofer response that will complement the main speaker response.

[0005] In light of these problems, there is a need in the art for asubwoofer response determining system (commonly referred to as acrossover) that produces a proper blending of the subwoofer sonic outputand the main speaker sonic output.

SUMMARY

[0006] The present invention provides a system and method for accuratelyreproducing audio sounds by adjusting the response characteristics of asubwoofer to produce a proper blending of sound from a subwoofer and amain speaker in a sound reproduction system.

[0007] In architecture, the system comprises a compensation circuitconfigured to produce a desired low-frequency signal from an inputsignal in response to user adjustable settings that are indicative ofmain speaker response characteristics. The desired low-frequency signal,when cascaded through the subwoofer amplifier and the subwoofer,produces a subwoofer sonic output that, when combined with the mainspeaker sonic output, produces a more desirable blending ofhigh-frequency and low-frequency sounds (i.e., a higher quality sound).

[0008] In accordance with another aspect of the present invention, amethod is provided for accurately producing audio sounds by adjustingthe low-frequency sonic output of a subwoofer. In the method, a desiredlow-frequency signal is produced in response to user adjustable settingsthat are indicative of main speaker characteristics. The desiredlow-frequency signal is produced by subtracting a signal indicative ofthe main speaker response from a signal indicative of the desiredcombined subwoofer-main speaker response.

[0009] Other systems, methods, features, and advantages of the inventionwill be or become apparent to one with skill in the art upon examinationof the following figures and detailed description. It is intended thatall such additional systems, methods, features, and advantages beincluded within the scope of the invention, and be protected by theaccompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The above and further features, advantages, and benefits of thepresent invention will be apparent upon consideration of the followingdetailed description, taken in conjunction with the accompanyingdrawings, in which like reference characters refer to like partsthroughout.

[0011]FIG. 1 is a frequency response plot showing a combinedsubwoofer-main speaker frequency response.

[0012]FIG. 2 is a simplified block diagram showing a crossover inrelation to components of a typical audio system.

[0013]FIG. 3 is a diagram of a front panel of the preferred crossover,configured to receive user adjustable settings.

[0014]FIG. 4A is a block diagram showing a simplified architecture of acompensation circuit having a desired transfer function circuit, amain-speaker equivalent circuit, and a summing circuit.

[0015]FIG. 4B is a block diagram showing an example system of FIG. 4Ahaving an all-pass filter as a desired transfer function circuit and a2^(nd)-order high-pass filter as an analog of the main speaker high-passfunction.

[0016]FIG. 5A is a circuit diagram showing the all-pass filter of FIG.4B in more detail.

[0017]FIG. 5B is a circuit diagram showing the high-pass filter of FIG.4B in more detail.

[0018]FIG. 5C is a circuit diagram showing the summing circuit of FIG.4B in more detail.

[0019]FIG. 6A is a circuit diagram showing an equivalent-resistancecircuit that can be used for the first resistor (R1) in FIG. 5A.

[0020]FIG. 6B is a circuit diagram showing an equivalent-resistancecircuit that can be used for the third resistor (R3) in FIG. 5B.

[0021]FIG. 6C is a circuit diagram showing an equivalent-resistancecircuit that can be used for the fourth resistor (R) in FIG. 5B.

[0022]FIG. 6D is a block diagram showing a microcontroller circuit forproviding a control voltage to the equivalent resistances of FIGS. 6A,6B, and 6C.

[0023]FIG. 7A is a flow chart showing the operation of the compensationcircuit of FIG. 4A.

[0024]FIG. 7B is a flow chart showing the production of thelow-frequency signal of FIG. 7A in more detail.

DETAILED DESCRIPTION OF DRAWINGS

[0025] Having summarized various aspects of the present invention,reference will now be made in detail to the description of the inventionas illustrated in the drawings. While the invention will be described inconnection with these drawings, there is no intent to limit it to theembodiment or embodiments disclosed therein. On the contrary, the intentis to cover all alternatives, modifications, and equivalents includedwithin the spirit and scope of the invention as defined by the appendedclaims.

[0026] Theory

[0027] The normal audible sound spectrum consists of a frequency rangefrom approximately 20 Hz up to approximately 20 kHz. Since speakers in atypical stereo system do not have a uniform frequency response to thelowest parts of the audible sound range, the low-frequency components ofthe sound range may be reproduced by different speakers having asuperior low-frequency response. An example of this is given in FIG. 1,which is a frequency response plot showing the high-frequency andlow-frequency components of a signal. Ideally, a crossover alters auniform input signal 150 into a low-frequency signal 130 havingfrequencies below the given frequency 105. The input signal 150 isamplified through a main speaker amplifier while the low-frequencysignal 130 is amplified through a subwoofer amplifier. The signal fromthe main speaker amplifier is then channeled through a main speakerwhich provides the high-frequency signal 140, determined by itslow-frequency characteristics. Similarly, the signal from the subwooferamplifier is channeled through a subwoofer which provides the lowfrequency sounds.

[0028] Since the combined output 150 of the subwoofer and the mainspeaker is the sum of the high-frequency component 140 and thelow-frequency component 130, if a desired combined output 150 is knownand the actual high-frequency output 140 of the main speaker is alsoknown, then an appropriate low-frequency signal 130 having the desiredlow-frequency characteristics may be produced by subtracting thehigh-frequency output 140 from the desired combined output 150.

[0029] The present invention provides such a system and method forproducing such a desired low-frequency signal from a crossover. Thedetails of the invention, discussed below, are not to be taken in alimiting sense but are made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe ascertained with reference to the issued claims.

[0030] Crossover for Producing a Desired Low-Frequency Signal

[0031] Turning now to the system of the invention, FIG. 2 shows ahigh-level diagram of a sound system utilizing the present invention.The sound system includes the crossover 200 designed to incorporateinformation about the frequency response of a main speaker 280 (i.e., toimplement the compensation technique discussed above). The crossover 200comprises a user interface 205 that allows a user to input variousparameters related to the main speaker 280. These parameters reflect thedegree of adjustment needed to compensate for actual frequency responsecharacteristics of the main speaker 280 as described in FIG. 1. Thecrossover 200 receives an input signal 210 and produces the desiredlow-frequency signal 230. The input signal 210 is also sent to a mainspeaker amplifier 240, which amplifies the input signal 220 to producean amplified input signal 260. The amplified input signal 260 is thensent to a main speaker 280 for the production of sound. The desiredlow-frequency signal 230 is cascaded through a subwoofer amplifier 250configured to amplify the desired low-frequency signal 230, and theresulting amplified low-frequency signal 270 is then sent to a subwoofer290 configured to produce the low-frequency sounds. The desiredlow-frequency signal 230 produced by the crossover 200 takes intoaccount the low-frequency range that is produced by the main speaker280. Hence, the blending of the subwoofer's sonic output with the mainspeaker's sonic output produces the desired combined sonic output.

[0032] Although the crossover 200 is shown as a separate component, itmay be integrated with other components of the speaker system. Forexample, the crossover 200 and subwoofer amplifier 250 may be integratedinto a single unit or, alternatively, the crossover 200 and main-speakeramplifier 240 may be integrated into a single unit. Moreover, althoughthe current embodiment only shows a low-frequency output, it will beclear to one of ordinary skill in the art that a high-frequencycomponent may also be produced by the crossover. It will also be clearto one of ordinary skill in the art that the inventive nature does notdepend on the possible permutations by which the crossover may becombined with other sound system components.

[0033]FIG. 3 shows a front panel, or user interface 205, of a crossover200 (FIG. 2) in the sound system of FIG. 2. The user interface 205allows the user to control many parameters associated with the soundreproduction system such as configuration parameters 315, systemparameters 325, or main speaker characteristics 335. The configurationparameters 315 typically include mode (e.g., augment or crossover),channel (e.g., stereo or mono), number of subwoofers, and main amplifiergain. System parameters 325 may include low frequency extension, lowfrequency level, and crossover frequency. Main speaker characteristics335 may include type (e.g., sealed or reflex), low frequency limit,sensitivity, and damping factor. These parameters are adjusted usingselection buttons 345 configured to select the parameter to be adjusted,and adjust buttons 355 configured to adjust those selected features. Adisplay 385 on the user interface 205 apprises the user of the changingparameters. Once the system parameters are set using the selectionbuttons 345 and the adjust buttons 355, the user may store theparameters using a store button 365. Alternatively, once certainparameters have been stored, the user may recall the stored parametersusing a recall button 375.

[0034] Although several parameters and options are shown in the exampleuser interface 205, it will be clear to one of ordinary skill in the artthat the user interface 205 may be more or less complex depending on theoptions available for such a system. For purposes of this discussion,the parameters of interest are configuration mode (specifically, augmentmode) and the main speaker characteristics 335. Upon selection ofaugment mode (configuration parameter 315), the user may enter mainspeaker characteristics 335 (e.g., type, low frequency limit,sensitivity, damping factor, etc.) related to known characteristics ofthe main speaker 280 (FIG. 2). Responsive to the user's input of themain speaker characteristics 335, the crossover 200 adjusts thelow-frequency response of the crossover 200 (FIG. 2) in response tothese main speaker characteristics so that the crossover 200 (FIG. 2)produces a desired low-frequency component 230 (FIG. 2) of the signal.The desired low-frequency component 230 (FIG. 2), when cascaded throughthe subwoofer amplifier 250 (FIG. 2) and the subwoofer 290 (FIG. 2),produces a response that, when combined with the main speaker response,produces an ideal combined response (i.e., a desirable blending ofsound). Although the front panel (or user interface) is shown in thepresent embodiment as having configuration parameters, systemparameters, and main speaker characteristics, it will be clear to one ofordinary skill in the art that additional user options may beimplemented through the user interface. These user options may include,but are not limited to, acoustics of the room, temperature, number ofspeakers, etc. Similarly, it will be clear to one of ordinary skill inthe art that several options may be removed from the user interface inorder to reduce the complexity of the system for the user. Although onlycertain options are shown in the user interface, it is not intended tolimit the invention to only those options. On the contrary, the intentis to cover all alternatives, modifications, and equivalents includedwithin the spirit and scope of the invention as defined by the appendedclaims.

[0035] Turning now to the details of a system for generating the desiredlow-frequency signal in response to the user inputs indicative ofmain-speaker low-frequency characteristics, FIG. 4A shows an embodimentof the invention as a compensation circuit 400 a configured to producethe desired low-frequency signal 230 (FIG. 2). In this embodiment, aninput signal 210 is passed through a desired transfer function circuit410 a, which produces a desired system signal 415 having thecharacteristics of a desired combined subwoofer-main speaker signal 150(FIG. 1). The desired system signal 415 is then transmitted to a summingcircuit 430.

[0036] The input signal 210 is also passed through a main-speakerequivalent circuit 420 a, which produces a main-speaker equivalentsignal 425 having the low-frequency characteristics of a signal producedby a main speaker (e.g., 140 of FIG. 1). This main-speaker equivalentsignal 425 is also transmitted to the summing circuit 430. The summingcircuit 430 receives both the desired system signal 415 and themain-speaker equivalent signal 425, and subtracts the main-speakerequivalent signal 425 from the desired system signal 415 to produce asubtracted signal 430. The amplitude of the subtracted signal 430 isadjusted by a gain adjusting circuit 440, which is typically a variableresistor, to produce a desired low-frequency signal 230. As seen fromFIG. 4A, rather than directly setting the characteristics for thelow-frequency signal (e.g., directly setting a high-frequency roll-offor directly setting low-pass characteristics) as is done in typicalsubwoofer systems, this invention generates the desired low-frequencysignal 230 from known characteristics of the main speaker so as tobetter compensate for main-speaker low-frequency characteristics and,therefore, producing a better blend of sound from the main speaker andthe subwoofer.

[0037] The compensation circuit 400 a of this invention can be bestdemonstrated by using a specific example. FIGS. 4B, 5A, 5B, 5C, 6A, 6B,6C, and 6D provide the specific example illustrating the constructionand operation of the compensation circuit 400 a illustrated in FIG. 4A.This example is not provided to limit the invention to the specificdetails but, rather, to more clearly illustrate the operation of certainaspects of the invention.

[0038]FIG. 4B is a specific example of the compensation circuit 400 a ofFIG. 4A. In this example, the main speaker response is represented as a2^(nd)-order high-pass filter 420 b having a cutoff frequency of F_(sp)and a damping factor of Q_(sp). In a preferred embodiment, a desiredcombined subwoofer-main speaker response 150 (FIG. 1) would berepresented by a 2^(nd)-order all-pass filter having a characteristicfrequency, F_(ap), of: $\begin{matrix}{F_{ap} = \frac{F_{sp}}{2Q_{sp}}} & \left\lbrack {{Eq}.\quad 1} \right\rbrack\end{matrix}$

[0039] Once the cutoff frequencies and damping factors of the mainspeaker response and the desired combined response are known, thesefactors are used to create the compensation circuit 400 a (FIG. 4A)configured to produce the desired low-frequency signal 230 in responseto the main-speaker low-frequency characteristics.

[0040] Continuing with this example, FIG. 5A shows a 2^(nd)-orderall-pass filter 410 b that may be used to produce the desired all-passresponse of FIG. 4B. The all-pass filter 410 b comprises an operationalamplifier 525, a variable resistor 522 with a resistance of R₁, acapacitor with a capacitance of C₁, and two fixed resistors 524, 528with a resistance of R₂, configured to achieve the desired 2^(nd)-orderall-pass characteristics. The characteristic frequency of the all passfilter is given by Eq. 2 as: $\begin{matrix}{F_{ap} = {\frac{1}{2\pi \quad C_{1}R_{1}}.}} & \left\lbrack {{Eq}.\quad 2} \right\rbrack\end{matrix}$

[0041] And, since in this example it is desired that the all-passfrequency be set according to Eq. 1, the variable resistance, R₁, may berepresented as: $\begin{matrix}{R_{1} = {\frac{Q_{sp}}{C_{1}\pi \quad F_{sp}}.}} & \left\lbrack {{Eq}.\quad 3} \right\rbrack\end{matrix}$

[0042]FIG. 5B shows a 2^(nd)-order high-pass filter 420 b that may beused to produce the equivalent main-speaker response 425 (FIG. 4B) ofFIG. 4B. The example 2^(nd)-order high-pass filter 420 b comprises twoRC circuits 530, 540 serially connected to the input of the operationalamplifier 545 to produce the desired 2^(nd)-order characteristics. Ifidentical capacitors 533, 543 are used in each of the RC circuits 530,540, and the capacitor value and resistor values are C₂, R₃, and R₄,respectively, then the characteristic frequency, F_(sp), and the dampingfactor, Q_(sp), are given by Eq. 4 and Eq. 5, respectively, as:$\begin{matrix}{{F_{sp} = \frac{1}{2\pi \quad C_{2}\sqrt{R_{3}R_{4}}}}\text{and}} & \left\lbrack {{Eq}.\quad 4} \right\rbrack \\{Q_{sp} = {\frac{\sqrt{\frac{R_{4}}{R_{3}}}}{2}.}} & \left\lbrack {{Eq}.\quad 5} \right\rbrack\end{matrix}$

[0043] Thus, the values of R₃ (536 of FIG. 5B) and R₄ (546 of FIG. 5B)in terms of F_(sp) and Q_(sp) would be: $\begin{matrix}{{R_{3} = \frac{1}{4\pi \quad C_{2}Q_{sp}F_{sp}}}\text{and}} & \left\lbrack {{Eq}.\quad 6} \right\rbrack \\{R_{4} = {\frac{Q_{sp}}{C_{2}\pi \quad F_{sp}}.}} & \left\lbrack {{Eq}.\quad 7} \right\rbrack\end{matrix}$

[0044]FIG. 5C shows a summing circuit 430 that may be used to subtractthe equivalent main-speaker signal 425 from the desired system signal415. The summing circuit 430 comprises an operational amplifier 555configured as an adder circuit with four fixed resistors 552, 554, 556,558. Since adder circuits are well known in the art, details of addercircuits will not be further discussed.

[0045] A convenient way to achieve adjustable values of R₁ (522 of FIG.5A), R₃ (536 of FIG. 5B), and R₄ (546 of FIG. 5B) is to realize themwith voltage controlled equivalent resistances. This is shown in FIGS.6A, 6B, 6C, and 6D.

[0046]FIGS. 6A, 6B, and 6C show the resistors R₁ (522 of FIG. 5A), R₃(536 of FIG. 5B), and R₄ (546 of FIG. 5B) as voltage-controlledequivalent resistances, each implemented with two operationaltransconductance amplifiers 620 a, 640 a, 620 b, 640 b, 620 c, 640 c.Details on the operation of transconductance amplifiers are well knownand understood by persons skilled in the art, and need not be describedherein. Given the circuit configurations of FIGS. 6A, 6B, and 6C, theresistances R₁, R₃ and R₄ are represented by: $\begin{matrix}{{R_{1} = \frac{2R_{7}R_{8}}{{gm}\quad R_{6}V_{1}}},} & \left\lbrack {{Eq}.\quad 8} \right\rbrack \\{{R_{3} = \frac{2R_{7}R_{9}}{{gm}\quad R_{6}V_{3}}},\text{and}} & \left\lbrack {{Eq}.\quad 9} \right\rbrack \\{{R_{4} = \frac{2R_{7}R_{10}}{{gm}\quad R_{6}V_{4}}},} & \left\lbrack {{Eq}.\quad 10} \right\rbrack\end{matrix}$

[0047] where V₁, V₃, and V₄ are the control voltages and gm is thetransconductance per current through the resistors R₈ (690 of FIG. 6A),R₉ (693 of FIG. 6B) and R₁₀ (696 of FIG. 6B). Thus, the requiredvoltages V₁, V₃, and V₄, in terms of F_(sp) and Q_(sp), would be:$\begin{matrix}{{V_{1} = \frac{2R_{7}R_{8}\pi \quad C_{1}F_{sp}}{({gm})R_{6}Q_{sp}}},} & \left\lbrack {{Eq}.\quad 11} \right\rbrack \\{{V_{3} = \frac{8R_{7}R_{9}\pi \quad C_{2}F_{sp}Q_{sp}}{({gm})R_{6}}},\text{and}} & \left\lbrack {{Eq}.\quad 12} \right\rbrack \\{V_{4} = {\frac{2R_{7}R_{10}\pi \quad C_{2}F_{sp}}{({gm})R_{6}Q_{sp}}.}} & \left\lbrack {{Eq}.\quad 13} \right\rbrack\end{matrix}$

[0048]FIG. 6D shows a microcontroller 605 that may be used inconjunction with the equivalent resistance circuits of FIGS. 6A, 6B, and6C. In practice, it is convenient to use a microcontroller 605 toperform the calculations so that user-adjustable controls for F_(sp) andQ_(sp) can supply voltages to the micro-controller 605, and themicrocontroller 605 will supply outputs V₁ 610, V₃ 615, and V₄ 620according to Eqs. 11, 12, and 13, respectively. Since the structure andoperation of microcontrollers are well known in the art, these deviceswill not be discussed further. It is sufficient to say that carefuladjustment of voltages V₁ (610 of FIGS. 6A and 6D), V₃ (615 of FIGS. 6Band 6D) and V₄ (620 of FIGS. 6C and 6D) produces the desired resistancesR₁ (522 of FIG. 5A), R₃ (536 of FIG. 5B), and R₄ (546 of FIG. 5B),which, in turn, are used to construct the 2^(nd)-order all-pass filter410 b (FIG. 4B) and the 2^(nd)-order high-pass filter 420 b (FIG. 4B)used in the production of the desired low-frequency signal 230.

[0049] As shown from the above embodiment of the invention, the userinputs indicative of the main speaker characteristics may be translatedto adjustable voltages V₁, V₃, and V₄, which determine the variableresistances in the above-described circuits. These voltages aresubsequently used to produce a desired all-pass response circuit, whichhas, as an output, the desired characteristics of the combined signal.Furthermore, these adjustable voltages are used to produce theequivalent main-speaker response circuit, which produces a main-speakerequivalent output. The desired low-frequency output is produced as afunction of the main-speaker low-frequency characteristics and,therefore, will produce a better blending of sound when finally combinedwith the main-speaker sonic output.

[0050] Method Steps for Producing the Desired Low-Frequency Signal

[0051]FIG. 7A shows the operation of the above-described embodiment ofthe invention. As an initial matter, the main speaker outputcharacteristics are determined in step 710. User-adjustable settings,which are indicative of main speaker characteristics, are then definedin step 720. These user-adjustable settings may include, but are notlimited to, the cutoff frequency of the main speaker, the damping factorof the main speaker, a sensitivity factor, an enclosure type (e.g.,sealed or reflex), a gain factor, or any number of other factors asdescribed above with reference to FIG. 3. Once these user-adjustablesettings have been defined 720, these settings are input, in step 730,into the compensation circuit via a user interface similar to thatdescribed with reference to FIG. 3. The compensation circuit thenproduces, in step 750, the desired low-frequency signal in response tothe user-adjustable settings, which are indicative of main-speakerlow-frequency characteristics. This method, unlike conventional methodsof adjusting a subwoofer response, takes into consideration themain-speaker low-frequency characteristics in determining the output ofthe subwoofer. Thus, this method results in a better blending of soundfrom the subwoofer-main speaker combination.

[0052]FIG. 7B shows the step of producing 750 (FIG. 7A) the desiredlow-frequency signal in more detail. Once the user-adjustable settingsthat are indicative of main-speaker low-frequency characteristics havebeen input 730 (FIG. 7A) into the compensation circuit via the userinterface, the compensation circuit 400 a (FIG. 4A) generates, in step753, a desired combined system signal (which reflects the desired output415 (FIG. 4A) from a subwoofer-main speaker combination) from theuser-adjustable settings. The compensation circuit 400 a (FIG. 4A)further generates, in step 756, an equivalent main-speaker signal 425(FIG. 4A) from the user adjustable settings. Once these two signals havebeen generated 753, 756, the compensation circuit subtracts, in step759, the equivalent main speaker signal 425 (FIG. 4A) from the desiredsystem signal 415 (FIG. 4A). This subtracted signal 430 (FIG. 4A) may bedirectly used as the desired low-frequency signal 230 (FIG. 4A) or,alternatively, may be adjusted using a gain adjusting circuit 440 (FIG.4A) prior to being used as the desired low-frequency signal. In eithercase, the step of subtracting 759 produces a low-frequency signal havingthe desired characteristics which will produce the appropriatelow-frequency sonic output which will in turn, when combined with themain-speaker sonic output, produce the desired combined sonic output(i.e., the desired blending of sound).

[0053] Although an exemplary embodiment of the present invention hasbeen shown and described, it will be apparent to those of ordinary skillin the art that a number of changes, modifications, or alterations tothe invention as described may be made, none of which depart from thespirit of the present invention. For example, the compensationmechanism, although described as an analog circuit, may be implementedby digital means, the order of the filters may be adjusted depending onthe response of the actual system components, the method steps may berearranged, etc. All such changes, modifications, and alterations shouldtherefore be seen as within the scope of the present invention.

I claim:
 1. A system for adjusting the frequency response of subwoofersystems comprising: a user interface configured to receiveuser-adjustable variables indicative of main speaker characteristics;and a compensation circuit configured to produce a desired low-frequencysignal from an input signal in response to the user-adjustablevariables.
 2. The system of claim 1, wherein the main speakercharacteristics comprise low-frequency characteristics of the mainspeaker.
 3. The system of 1, wherein the user adjustable variablescomprise a low-frequency cutoff frequency.
 4. The system of 1, whereinthe user adjustable variables comprise a low-frequency damping factor.5. The system of 1, wherein the user adjustable variables comprise aspeaker sensitivity factor.
 6. The system of 1, wherein the useradjustable variables comprise an enclosure type.
 7. The system of 1,wherein the user adjustable variables comprise a gain factor.
 8. Amethod for adjusting the frequency response of subwoofer systems,comprising the steps of: inputting user adjustable settings indicativeof main speaker characteristics; and producing a desired low-frequencysignal in response to the user adjustable settings.
 9. The method ofclaim 8, wherein main speaker characteristics comprise low-frequencycharacteristics of the main speaker.
 10. The method of claim 8, whereinthe main speaker characteristics comprise a low-frequency cutofffrequency.
 11. The method of claim 8, wherein the main speakercharacteristics comprise a low-frequency damping factor.
 12. The methodof claim 8, wherein the main speaker characteristics comprise a speakersensitivity factor.
 13. The method of claim 8, wherein the main speakercharacteristics comprise an enclosure type.
 14. The method of claim 8,wherein the main speaker characteristics comprise a gain factor.
 15. Asystem for adjusting the frequency response of subwoofer systems,comprising: means for inputting a plurality of user adjustable settingindicative of main-speaker characteristics; means for receiving an inputsignal; and means for producing a desired low-frequency signal from theinput signal in response to the plurality of user adjustable setting.16. The system of claim 15, wherein the main speaker characteristicscomprise low-frequency characteristics of the main speaker.
 17. Thesystem of claim 15, wherein the means for producing the desiredlow-frequency signal further comprises means for setting a low-frequencycutoff-frequency of the main speaker.
 18. The system of claim 15,wherein the means for producing the desired low-frequency signal furthercomprises means for setting a low-frequency damping factor of the mainspeaker.
 19. The system of claim 15, wherein the means for producing thedesired low-frequency signal further comprises means for setting a gainof the main speaker.